This invention relates to an ion source and more particularly to an atomic level ion source (ALIS) generating ions from a volume near the size of a single atom. The source of the invention can be used as the particle source in a charged particle microscope.
Charged particle microscopes typically use electrons or metal ions. Both microscopes are very well developed and reliable; however, the electron microscope has the highest resolution. An ALIS-type helium ion microscope would have a distinct advantage over electrons that are now in use in charged particle microscopes. Light ions significantly reduce the optical diffraction effects that electrons cause and they have a smaller interaction volume when focused onto the surface of a sample by a lens. Helium ions can also provide better chemical contrast than can electrons. Also, the source size is smaller than electron sources providing a smaller final spot size for a given optical condition. It is also believed that the coherence, or energy spread, of this type of ion source is better than electron sources minimizing chromatic aberration effects that cause resolution reduction.
Previous attempts have been made to produce a reliable atomic level ion source for use in a microscope application. For example, the Max Planck Institute is likely to be considered the most successful group for exploring such an ion source but the group failed at producing a reliable recipe for stable and repeatable commercial operation.
It is therefore an object of the invention to provide a very bright ion source that emits ions from an area near the size of an atom dimension because resolution is improved as ion source size is reduced and as brightness increases. Such a source incorporated into a typical ion electro-optical system will provide very high resolution pictures having near atom resolution.